Progressive pseudorheumatoid arthritis of childhood (PPAC). A hereditary disorder simulating rheumatoid arthritis.

Five patients are described with a hereditary arthropathy affecting major and minor joints. The main features of this progressive connective tissue disorder are restricted joint mobility, osseous swelling of the interphalangeal and other joints, and platyspondyly. The condition is commonly misdiagnosed as "chronic juvenile polyarthritis with Scheuermann disease". It differs from the rheumatoid-factor-negative polyarticular form of rheumatoid arthritis and other rheumatoid spondylarthropathies by the absence of arthritic and other inflammatory changes, radiographically by the absence of destructive and the presence of dysplastic bone changes. The disorder does not seem to respond to the usual forms of antirheumatoid treatment. Histological studies showed a peculiar, nest-like clustering of chondrocytes in the resting and growth cartilage suggesting that pathogenetically this is a primary disorder of the articular cartilage.